This invention relates to an apparatus and method #or opening signature sheets preparatory to transport of the signature to a thread sewing machine.
A signature is comprised o one or more folded sheets, each of which is subdivided into a plurality of signature sheets bounded by fold lines. The fold lines are perforated to facilitate separation of the signature sheets at a later stage in a book manufacturing process.
In opening a signature, the object is to get to the "center," defined herein as the fold line disposed along the spine of the signature dividing it into an equal number of signature sheets, excluding endsheets, on either side of the line. Various systems for accomplishing this purpose are known in the art.
For instance, U.S. Pat. No. 4,275,873 to Rathert discloses a signature feeder wherein signatures are transported in a substantially vertical orientation by a conveyor. A stationary suction block positioned alongside the conveyor opens the outermost page of the signature by applying suction to a lowermost corner thereof, and this process is repeated sequentially with other suction blocks until the "center" is reached.
U.S. Pat. No. 4,463,941 to Schlough discloses an apparatus and methods for opening folded sheets wherein the sheets are transported in a substantially horizontal manner. In the second of the two methods, a vacuum system including a rotary wheel is disposed above a folded sheet being conveyed. The wheel has suction openings enabling the wheel to grip the top page of the folded sheet, thereby opening it. Additionally, a vacuum block is disposed below the bottom page of the folded sheet to grip it, thereby facilitating the opening.
U.S. Pat. No. 4,127,261 to Meratti teaches a device for opening signatures wherein a rotating operative member is provided with supply and take-up reels carrying a roll of pressure-sensitive adhesive tape. The tape passes over a smaller guide roller mounted to the operative member, and the adhesive side of the tape at that location functions as an operative surface engaging the surface of an uppermost signature sheet when a plate positioned alongside the conveying path raises the signature from the conveying surface. Continued rotation of the operative member causes opening of the signature sheet.
U.S. Pat. No. 4,470,588 to Geiser discloses a device for opening folded paper sheets whereby suction devices orbit about axes which are somewhat vertical, being inclined with respect to a vertical axis. Each suction head is located at a terminus of an arm that is 90.degree. to the slanted axis of rotation. Therefore, a suction head moves upwardly during orbital movements of a suction device. This attracts an outermost layer of a folded sheet as it approaches and flexes it outwardly, whereby the inner side of the layer can be intercepted by a stationary retaining element following the respective suction head.
Other machines, while being compact and occupying minimal floor space, have a problem in handling signatures with weak, easily broken, perforations. The handling of such signatures by these machines is such that the machine breaks the perforations, causing misalignment of the signature with respect to a transporting saddle and/or falling of the signature from the saddle. This necessitates that signatures of this type be handfed, significantly reducing production.
While machines such as that disclosed by Rathert employ stationary suction devices to open signatures, the considerable length between the feeding hopper and the sewing station causes occupation of a large amount of floor space and requires frequent back-and-forth trips by the machine operator.
There is a need in the art for a single, compact apparatus which is adaptable to open differing types of signatures. Signatures vary widely in terms of weight, porosity, thickness, and number of sheets and in terms of the strength of the perforations along the folding lines. Such varied signatures, which occur primarily in the United States, cannot be consistently opened by conventional signature feeder machines predominantly constructed by European manufacturers. Moreover, 4-page signatures have been known to become airborne due to their light weight.